To save the added weight of an additional pack pack you could place your minimalist gear (compass, space blanket, mirror, match safe. & sak or leatherman, etc) in your first aid kit. Place that in your ruck last so that it's right on top. If for any reason you need to lighten up in a hurry all you need to grab is the one pouch. Like you, I can't really see the need for this arising but being prepared should also cover the situations we don't see coming.

** A big thanks to Adventure Medical, whose essentials concept I just plagiarized.

Ed